Sawdust as an Adsorbent for the Removal of Methylene Blue ...

JOURNAL OF CHEMICAL ENGINEERING VOL. 1, NO. 1, JANUARY 2012

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Sawdust as an Adsorbent for the Removal

of Methylene Blue from Aqueous Solution:

Adsorption and Equilibrium Studies . Suleiman Idris, Muhammed M. Ndamitso, Yahaya A. Iyaka and Etsuyankpa B. Muhammad

Abstract - The present research indicated that

activated carbon prepared from saw dust has been

used to adsorb methylene blue (MB) from aqueous

solution using NaOH as an activating agent at initial

concentration of 10-50 mg/L. Percentage carbon yield

decrease with increase in activation burn off time

since more volatiles are release from the char. The pH

range of 7.81±0.01 to 7.83±0.02 obtained by activated

carbons prepared from saw dust is suitable for MB

removal from aqueous solution since for most

application, activated carbon pH of 6-8 is acceptable.

Adsorption capacity at equilibrium (qe) tend to

increases with increases in initial concentration from

10 – 50 mg/L with higher MB removal of 99.67 %

recorded. Adsorption isotherm which include

Langmuir, Freundlich, Temkin and Harkin’s – Jura

were used to analysed the equilibrium data.

Langmuir isotherm best described the adsorption

data with higher correlation coefficient R2 values (R2

= 0.982, R2 = 0.996 and R2 = 0.995) and RL values less

than one (RL= 0.009, RL = 0.001 and RL= 0.001) for

SD/NaOH/5, SD/NaOH/10 and SD/NaOH/15

activated carbon respectively.

Keywords- Adsorption capacity, Correlation

coefficient, Equilibrium, Harkin’s-Jura.

I. INTRODUCTION

Methylene blue (MB) is a heterocyclic aromatic

chemical compound with molecular formula:

Manuscript submitted on January 9, 2012. Sawdust as an

Adsorbent for the Removal of Methylene Blue from Aqueous Solution: Adsorption and Equilibrium Studies.

S. Idris is with the Department of Chemistry Federal University

of Technology P. M. B. 65 Minna, Niger State Nigeria

(+2348065699124;e-mail: [email protected]).

M. M. Ndamitso is with the Department of Chemistry Federal University of Technology P. M. B. 65 Minna, Niger State

Nigeria (e-mail: [email protected]).

Y. A. Iyaka is with the Department of Chemistry Federal

University of Technology P. M. B. 65 Minna, Niger State Nigeria (e-mail: [email protected]).

E. B. Muhammad is with the Center for Preliminary and Exral

Moral Studies, Federal University of Technology P.M. B.65,

Minna, Niger State Nigeria (e-mail: [email protected]).

C16H18N3SCl. At room temperature it appears as a

solid, odorless, dark green powder, that yields a

blue solution when dissolved in water. MB is an

important basic dye widely used for coloring paper,

temporary hair colorant, coating for paper stock,

dyeing, printing cotton and tannin, dyeing leather,

used as an antiseptic and for other medicinal

purposes (Methylene blue, 2011).

The release of dyes into wastewaters from

textile, cosmetic, paper and coloring industries

poses serious environmental problems. The

coloration of the water by the dyes causes

inhibitory effect on photosynthesis affecting

aquatic ecosystems (Theivarasu et al.,2011).

Adsorption of methylene blue from the aqueous

phase is a useful toll for product control of

adsorbents. Some kinds of sawdust have been

studied as adsorbents for removal of methylene

blue from aqueous solution (Rezal et al.,2011).

Adsorption using activated carbon is mostly

widely used method to remove dyes from aqueous

solution because of its low cost, ease of operation.

But its use is limited because of high cost and

associated problems of regeneration, there is a

constant search for cheaper substitutes. Many

efforts have been made to use low cost agro waste

materials in substitute for commercial activated

carbon. Some agro waste materials studied for their

capacity to remove dyes from aqueous solutions are

coir pith (Namasivayam and Kavitha, 2002), Cocoa

Shell (Theivarasu et al.,2011) etc.

The present research is to remove methylene

blue from aqueous solution using activated carbon

prepared from sawdust. Adsorption isotherm which

include Langmuir, Freundlich, Temkin and

Harkin’s- Jura were used to correlate the adsorption

data.

II. MATERIALS AND METHODS

A. Sample Collection and Preparation

The sawdust was obtained from Maitumbi

sawmill Kuta road Minna Niger State, Nigeria. The

methylene blue dye effluent was purchased from

Nahson medical equipment store, Hospital road,

mailto:[email protected]


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Minna, Niger State, Nigeria. The experiment took

place between April-September 2011.

The sawdust was sun dried, then oven dried at

100oC until properly dried. The sample was ground

and sieved with a 2 mm mesh size sieve. The less

than 2 mm samples were stored in airtight

container. Ash content was determined according

to the method described by AOAC (1990).

B. Preparation of Adsorbent

Activation involving two steps activation

process was adopted. 5 g of blended raw sample

was weighed into clean and pre-weighed crucibles.

They were introduced into a muffle furnace at

600oC for 5 minutes after which they were poured

from the crucible into a bath of ice water. The

excess water was drained off then carbonized

sample was washed, using 0.1 M HCl to remove

surface ash, followed by hot water wash and further

washing with distilled water to remove residual

acid. The sample was then sun dried, and further

dried in the oven at 1000C for one hour. This

process was repeated until a substantial amount of

carbonized sample was obtained.

Thereafter, 5g of already carbonized sample was

mixed with 5cm3

of activating agent (1M NaOH).

The sample was allowed to stand for 2 hours, after

which it was introduced into a furnace and heated

at 8000C for 5 minutes. The activated sample was

cooled with ice-cold water, excess water was

drained off and the sample dried at room

temperature. The above procedure was repeated for

different residual time (10 min and 15 min) until

substantial amount of activated carbon was

obtained. Washing was continue until the pH of

sample solution fall within 6-8, then the sample

was dried in an oven at 110oC overnight and stored

in air tight container (Rahman et al., 2005; Fan et

al., 2005).

C. Activated Carbon Characteristic

Bulk density (g/cm3) =

Weight of dry activated carbon(g) (1)

Volume of packed dry material(cm3)

(Apipreeya et al., 2006)

% Burn off = W0 – W1 X100 (2)

W0

W0= weight of char after pyrolysis, washing and

drying.

W1 = weight of carbon after activation, washing

and drying (Ioannidou and Zabaniotou, 2006).

% Yield = W1 X 100 (3)

W0

W0 = Original mass of precursor

W1 = weight of carbon after activation, washing

and drying (Yulu et al., 2001)

pH was determined using a pH meter and the

conductivity was taken using a conductivity meter

at room temperature (Okiemen et al., 2004).

D. Equilibrium Studies Using Batch Method

2g of activated carbon was interacted with 40

cm3 of methylene blue dye 10 ppm solution in a

beaker at 30oC. It was covered and allowed to stand

for 1 hour. It was than filtered using whatman filter

paper (No.42). The process was repeated at

different concentration (20, 30, 40 and 50 ppm).

Each mixture was separately filtered and the filtrate

was collected. The absorbance of the solution of

standard series and each filtrate after interaction

was taken using JENWAY spectrophotometer at

650 nm.

The amount of adsorption at equilibrium, qe (mg/g),

was calculated as follows:

qe = ( Co – Ce) V (4)

W

Co and Ce (mg/L) are the liquid-phase

concentration of dye at initial and equilibrium.

V(L) = volume of the methylene blue dye solution.

W(g) = weight of the activated carbon.

The percentage dye removal was calculated as:

% methylene blue removal = Co–Ce X100 (5)

Co

(Hameed, 2009)

E. Adsorption Isotherm

Adsorption isotherm is basically important to

describe how solutes interact with adsorbates, and

is critical in optimizing the use of adsorbents.

Langmuir Isotherm


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The Langmuir isotherm is based on the

assumption that it predicts monolayer coverage of

the adsorbate on the outer surface of the adsorbent

(Langmuir, 1918). This model also suggests that

there is no lateral interaction between the sorbed

molecules. Linear form of Langmuir isotherm is

1/qe = 1/KaqmCe + 1/qm (6)

Ka(L/mg) = Langmuir constant related to

adsorption capacity.

qm(mg/g) = Langmuir constant related to energy of

adsorption.

Langmuir constants Ka and qm can be calculated

from the slope and intercept of the plot of 1/qe

versus 1/Ce.

Freundlich isotherm

The Freundlich isotherm is based on multilayer

adsorption on heterogeneous surface

(Freundlich,1906). The linear form of Freundlich

equation is

lnqe = lnKF + 1/n lnCe (7)

KF (mg/g) = Freundlich constant indicating

adsorption capacity.

n = adsorption intensity.

Freundlich constant KF and n can be calculated

from the slope and intercept of the plot of lnqe

versus lnCe.

Temkin isotherm

The linear form of Temkin isotherm is given as

qe = B ln A + B ln Ce (8)

A(L/g) = Temkin constant related to maximum

binding energy.

B(J/mol) = Temkin constant related to heat of

sorption.

The plot of qe versus ln Ce enables the

determination of the constants A and B (Temkin

and Pyzhev, 1940).

Harkin’s – Jura isotherm

Harkin’s – Jura isotherm assumes the presence

of multilayer adsorption with the existence of

heterogeneous pore distribution (Gurses et al.,

2006). The linear form of the equation is given as

1/qe2 = (B/A) – (1/A(logCe)) (9)

Where A and B are the isotherm constants which

can be calculated from the slope and intercept of

the plot of 1/qe2 versus logCe.

III. RESULTS AND DISCUSSION

A. Characteristics of Activated Carbon

The percentage ash content of the sample was

low which is an indication of higher carbon yield

by the sample. The pH of the activated carbons

ranges from 7.81±0.01 to 7.83±0.02 respectively.

For most application activated carbon pH of 6-8 is

acceptable (Ahmedna et al.,2000). Percentage

carbon yield is the amount of original precursor

remaining after pyrolisis and activation treatment.

Percentage yield decrease as activation burn off

time increases which is as a result of more volatile

being released from the char, that is, as the

percentage activation burn off increases, the

percentage yield decreases. Carbon with an

adequate density also help to improve the filtration

rate by forming an even cake on the filter surface.

The American water work Association has set a

lower limit on bulk density at 0.25 g/cm3 for

granular activated carbons (GACs) to be of

practical use (American Water Works Association,

1991). The bulk density of the adsorbents fall

within the range of 0.25 ± 0.02 to 0.28 ± 0.01

g/cm3. The conductivity test is important because it

shows the presence of leach able ash which is

considered impurity and undesirable in activated

carbon (Khadija et al.,2007). The activated carbons

indicated the highest conductivity value of 5.80 ±

0.05 µS/cm which implies that the adsorbents

contain less leach able ash (Table 1).

TABLE 1

CHARACTERISTICS OF ACTIVATED CARBON

Parameter SD/NaOH/5 SD/NaOH/10 SD/NaOH/15

Activation burn off (%) 52.12 ± 0.02 56.00 ± 0.01 58.00 ± 0.01 Yield (%) 48.01 ± 0.01 44.11 ± 0.02 41.13 ± 0.01

Bulk density (g/cm3) 0.27 ± 0.01 0..28 ± 0.01 0.25 ± 0.02

Ph 7.81 ± 0.01 7.82 ± 0.01 7.83 ± 0.02 Conductivity (µS/cm) 3.60 ± 0.03 5.80 ± 0.05 4.70 ± 0.11


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B. Effect of Initial Dye Concentration

Fig. 1 indicates that an increase in initial MB

concentration leads to increase in the adsorption of

MB on saw dust. The adsorption capacity at

equilibrium increases from 0.20 to 0.99 mg/g with

an increase in the initial dye concentration from 10

to 50 mg/L. It is indicated that the activated

carbons prepared from saw dust yield better

adsorption of MB dye from aqueous solution, the

process attaining equilibrium gradually. This is due

to the fact that activated carbon is composed of

porous structure with large internal surface area.

Similar process was obtained on the adsorption of

MB on peanut hull (Gong et al., 2005).

Fig.1. Effect of initial dye concentration on equilibrium adsorption capacity.

C. Isotherm Analysis

Equilibrium data, commonly known as

adsorption isotherms, are basic requirements for the

design of adsorption systems (Ӧzer and Dursun,

2007). The equilibrium data for MB on saw dust

were modelled with the Langmuir, Freundlich,

Temkin and Harkin’s-Jura models.

Langmuir Isotherm

The linear plot of specific adsorption (1/qe)

against the equilibrium concentration (1/Ce) (Fig. 2,

Fig. 3 and Fig. 4) shows that the adsorption obeys

the Langmuir model. Langmuir constants qm and Ka

were determined from the slope and intercept of the

plot and are presented in Table II. The values of

correlation coefficient (R2 = 0.982, R

2 = 0.996 and

R2 = 0.995) obtained from Langmuir expression

indicates that Langmuir expression provided a

better fit to the experimental data of MB on saw

dust. The shape of the Langmuir isotherm was

investigated by the dimensionless constant

separation term (RL) to determine high affinity

adsorption and is expressed as RL = 1/ (1+KaC0).

RL values indicate the nature of adsorption to be

either be unfavourable (RL> 1), linear (RL=1),

favourable (0< RL < 1), or irreversible (RL = 0). The

RL values for the adsorption of MB onto saw dust

were 0.009, 0.001 and 0.001, indicating that the

adsorption was a favourable process.


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TABLE II

LANGMUIR ISOTHERM PARAMETERS

Parameters SD/NaOH/5 SD/NaOH/10 SD/NaOH/15

qm(mg/g) 0.76 0.76 0.67

Ka(L/mg) 2.18 18.94 13.95

R2 0.982 0.996 0.995

RL 0.009 0.001 0.001

Fig. 2. Langmuir adsorption isotherm of MB on activated carbon (SD/NaOH/5)



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Freundlich Isotherm

The equilibrium data were analyzed using the

linear form of Freundlich isotherm, by plotting ln

qe versus ln Ce (Fig.5, Fig.6 and Fig.7). The

Freundlich isotherm constants and the

corresponding correlation coefficient (R2) are

shown in Table III. The R2 values were higher ( R

2

= 0.948, R2 = 0.948, R

2 = 0.997) showing a good

linearity. n values show the type of isotherm to be

either favourable n >1 and unfavourable n < 1

(Alley, 2000). The findings revealed that the values

of n were greater than one ( n = 4.85, n = 3.70 and

n = 4.07) indicating that the dye adsorption is

favourable.

TABLE III

FREUNDLICH ISOTHERM PARAMETER


KF (mg/g) 0.54 0.77 0.65

n 4.85 3.70 4.07

R2 0.948 0.948 0.997


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Fig. 5. Freundlich adsorption isotherm of MB on activated carbon (SD/NaOH/5)



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Temkin Isotherm

The adsorption data were analysed by plotting qe

against ln Ce. The parameter of Temkin isotherm

were presented in Table IV. The R2 values were

also high (R2 = 0.915, R

2 = 0.905 and R

2 = 0.955)

indicating a good linearity.

TABLE IV

TEMKIN ISOTHERM PARAMETERS


A (L/g) 321.10 368.92 333.56

B (J/mol) 0.092 0.123 0.114

R2 0.915 0.905 0.955


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Fig. 8. Temkin adsorption isotherm of MB on activated carbon (SD/NaOH/5)



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Harkin’s – Jura Isotherm

The equilibrium data were also analysed by plot

of 1/qe2 versus log Ce. The parameters were

presented in Table V. The R2 values were also high

showing good linearity.

TABLE V

HARKIN’S-JURA ISOTHERM PARAMETERS


A 0.22 0.09 0.26

B 1.18 0.29 0.71

R2 0.938 0.925 0.977


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Fig. 11. Harkin’s – Jura adsorption isotherm of MB on activated carbon (SD/NaOH/5)



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Furthermore, the results revealed that the

Langmuir isotherm model was more suitable for

the experimental data than other isotherms because

of the high value of correlation coefficient (R2 =

0.982, R2 = 0.996 and R

2 = 0.995). This showed

that the adsorption of MB onto activated saw dust

occur as a monolayer adsorption on the adsorbent

surface. Demir et al. (2008) and Theivarasu and

Mylsamy, (2010) reported similar phenomenon.

IV. CONCLUSION

The findings revealed that methylene blue was

removed from aqueous using activated carbon

prepared from saw dust. Batch adsorption was

carried out at initial concentration of 10-50 mg/L.

Percentage carbon yield tend to decrease with

increase in activation burn off time since more

volatiles are release from the char. Adsorption

capacity at equilibrium also increases with

increases in initial concentration which result to

about 99.67 % MB removal. Langmuir,

Freundlich, Temkin and Harkin’s – Jura adsorption

isotherm were used to describe the equilibrium

data. Langmuir isotherm best described the

adsorption data with higher correlation coefficient

R2 values (R

2 = 0.983, R

2 = 0.996 and R

2 = 0.995)

and RL values less than one (RL= 0.009, RL =

0.001 and RL= 0.001) for SD/NaOH/5,

SD/NaOH/10 and SD/NaOH/15 activated carbon

respectively. The research further confirmed that

saw dust a low cost adsorbent could be employed

for the removal of MB with greater percentage

uptake.

APPENDIX

SD/NaOH/5, SD/NaOH/10 and SD/NaOH/15 are

saw dusts activated using NaOH as an activating

agent at the residual time of 5, 10 and 15 minutes

respectively.

Residual time is the time the activated carbon

spend in the furnace at 800oC to increase the

porosity and better adsorption site for the activated

carbon.

ACKNOWLEDGEMENT

The authors would like to acknowledge the

laboratory technologists, department of chemistry

federal university of technology, Minna Niger state,

Nigeria for their support during the course of the

research.

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ABOUT THE MAIN AUTHOR

NAME: Idris Suleiman

ADDRESS: Department of Chemistry Federal University of Technology Minna Niger State Nigeria.

Research Area: Adsorption of heavy metals using activated

carbon produced from animal and plant waste.

Sawdust as an Adsorbent for the Removal of Methylene Blue ...

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